The hoisting winch must be equipped with the following safety devices according to regulations: over-winding prevention device, over-speed prevention device, overload and under-voltage protection device, speed limiting device, brake shoe over-wear protection device, loose rope alarm device, full warehouse protection device and Depth indicator failure protection device and winch backup protection device, etc. The winches with a drum diameter of 0.8 m and below generally do not have the above safety devices due to their simple structure and slow running speed. Other winches are equipped with different types and numbers of safety devices according to different requirements.
The following is a brief introduction to the above-mentioned winch safety device.
(1) Anti-over-rolling device
When the lifting container exceeds the normal terminal parking position 0.5 m, the over-rolling protection device will act, cut off the main motor power supply, and activate the safety brake to achieve safe braking. The sensing element of the over-winding device generally adopts a travel switch. In addition to installing on the depth indicator, it should also be installed in the shaft to play a dual protection role.
(2) Anti-overspeed device
When the hoisting speed of the winch exceeds 15% of the maximum hoisting speed, the over-speed protection device will automatically work to cut off the main motor power supply and realize safe braking. Old-fashioned winches with a drum diameter of 1·2 m～1.6m have no overspeed protection device, and a centrifugal ball overspeed protection device is installed on the explosion-proof hydraulic winch.
(3) Speed limit protection device
For the winch with a lifting speed exceeding 3 m/s, a speed limit protection device must be installed to ensure that the speed of the lifting container before reaching the terminal parking position (that is, the deceleration stage) does not exceed 2 m/s. There are two types of speed-limiting devices: mechanical and electrical. The structure of mechanical speed-limiting devices is relatively complex, and the sensitivity and accuracy are poor. Therefore, electrical speed-limiting devices are mainly used at present.
(4) Overload and undervoltage protection device
Overload (that is, overcurrent) relay is directly connected in series in the main circuit or the secondary circuit of the current transformer. When the motor or other equipment fails, the motor current is greater than the set current value (generally 3 times the rated current), the relay action can cut off the power supply, ensuring the safety of electrical equipment and avoiding the expansion of accidents. The undervoltage protection device is in the power switch cabinet. When the power voltage fluctuates downward and exceeds the specified value, the power switch automatically trips and brakes safely.
